38 



NATURAL HISTORY OF THE FARM 



limpet-shaped. Two of these are shown in 

 Figure 19. In all of them flaring margins 

 of the body fit down closely to the stone and 

 deflect the water, so that it presses them 

 against their support. 

 Fig is Two -*- n st ^ water the deep pools are the 

 insect larvae that special home of the larger fishes. We shall 



stick to stones in r ° 



rapid water: o. the return to them in the next study. In the 



flat riffle - beetle J 



(Psephem^je^n- shoaler parts and in the midst of the aquatic 

 Zha eA m ) idge (BU ~ ve £ e t a ti° n are the lesser fishes and many other 

 familiar vertebrates, frogs and their tadpoles, 

 salamanders, turtles, etc., of uncertain occurrence. Much 

 more generally distributed and constantly present are a 

 few molluscs and crustaceans, such as are shown in Figure 

 20. There are a few adult insects (fig. 21) and many insects 

 in immature stages (figs. 22, 23) and 24. Some help toward 

 the recognition of these may be had from the table on pages 

 40 and 41, which contains brief hints, also, of the situation 

 they occupy in the water and the role they play in the food 

 consumption. 



There are leeches, and fresh-water sponges and bryozoans, 

 and a host of lesser forms of many groups, mostly too small to 



CRUSTACEANS 



Pig. 20. Some common crustaceans and molluscs: crawfish, with the asellus at 

 the left and the scud (Gammarus) at the right; — also, a mussel and two snails; 

 (Limnaa, on the left, and Planorbis on the right). 



